Volume control



3 Q o. o. WHELAN v 1,747,961

' VOLUMEVCONTROL I Filed Sept 26, 1928 Inventor: Dow O. Whelan,

z g I His Attorneg.

Patented Feb. 18, 1930 NITED STATES mar DOW 0. WHELAN, OF SCOTIA, NEW YORK, ASSIG-NOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK VOLUME CONTROL Application filed September 26, 1928. Serial No. 308,412.

The present invention relates to a volume control for radio-phonograph combinations in which, for example, as is well known, the audio-frequency apparatus of the radio receiver may be used for amplifying phonograph signals created by a suitable phonograph pick-up device.

Previous practice in connection with such radio-phonograph combinations has been to use two separate controls for volume, one for radio reception and one for phonograph records. XVith two controls, both of which adjust volume, one is always inoperative, and the user is often confused regarding which control to move in order to regulate the volume of the combination.

In radio-receiving apparatus the modern trend is toward simplicity in the design of the control panel and a minimum of control knobs. Hence from this standpoint of simplicity, the use of two volume control knobs is undesirable, in addition to being confusing to the user. It is also more costly to manufacture.

It is the object of this invention to provide an improved dual volume control means for radio-phonograph combinations whereby the volume control of such combination instruments may be operated by a single knob or other suitable single control means.

My invention will be better understood from the following description when considcred in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 is a schematic wiring diagram of a radio-phonograph combination provided with a volume control means embodying the invention; Fig. 2 is a sid view partly in section of the combination control means; and Fig. 3 is an end view of the same, on the same scale as Fig. 2.

Referring to Fig. 1,5, 6 and 7 are radiofrequency amplifier tubes connected 'in cascade through suitable tuned transformers 8 with a detector tube 9, which in turn feeds an audio-frequency amplifier comprising an amplifier tube 10 and an out-put tube 11 connected in cascade by suitable cou ling means such as audio frequency trans ormers 12.

The out-put tube 11 is connected with a reproducing device or loud speaker 13 and in the present example an out-put device such as an out-put transformer 14 is employed between tube 11 and the reproducing device.

The above described apparatus represents any radio-receiving apparatus adapted for phonograph combination, that is, having a suitable audio-frequency amplifier and reproducer. The receiver is supplied with energy from a suitable power supply device indicated at 15 which, as is well known, may comprise a suitable source of plate voltage together with means for supplying filament lighting current to the tubes of the set. In the present example the filament su ply leads from 15 are indicated at 16, 17 an 18 while the plate voltage supply leads are indicated at 19, 20 and 21. The source of power supply does not concern the invention and no further description thereof is believed to be necessary.

The radio volume is controlled by varying the radio-frequency input to the apparatus by means of a potentiometer 22 connected in the antenna circuit 23 in such a manner that the initial receiving tube 5 may have applied to its grid anv portion or all of the voltage set up by the drop through the potentiometer in the antenna circuit. This result is produced by moving a contact or contact arm 24 along the resistance of the potentiometer. The potentiometer 22 represents any suitable radio volume control means and is not necessarily confined to the antenna circuit or to the resistor type but may be of any suitable type. and may be located at any suitable point in the receiver as is well known.

The set is also provided with a suitable phonograph pick-up device .25 indicated in the present example as of the electromagnetic type, which delivers signal energy to a potentiometer or variable resistor 26 from which the signal energy is taken through an output circuit 27. i/Vith this arrangement one side of circuit 27 connects with the potentiometer arm 28 while the other side connects with one end of the potentiometer resistance, thus providing a variable volume control for phonograph operation. Out-put circuit 27 is whic connected with the initial audio-frequency transformer 12 through a switch 29 which may be moved to the closed position when usin the phonograph pick-up device, and

is normally moved to the open position'for radio reception. The direction of operation of the switch is indicated in the drawing and as shown is in a neutral position in which neither circuit is connected.

Connected with the switch 29 by suitable operating means 30 is a second switch 31 which preferably operates to open some portion of the receiving circuit such as the detector filament or the plate supply lead of the .radio frequency amplifiers when switch 29 is thrown to a position to connect the phonograph pick-up with the initial audio-frequen cy transformer 12. This prevents radio reception from interfering with the reproduction of phonographsignals and any suitable means of this character may be used.

Although this single control arrangement is not necessarily limited to the use of variable resistor or potentiometer type of controls, this type is simple and easily provided and particularly well adapted to present type radio receivers and phonograph pick-up devices. For other types of volume control the same arrangement may be used.-

With'the resistance type as shown and described it has been found in practice that potentiometer 22 has preferably about 2000 ohms total resistance while potentiometer 26 has about 60 ohms total resistance. These resistances are thus readily adapted to be provided in circular form of equal length or equal angular length whereby they may be operated by the same means throu h the same range. They may thus be mounte in tandem relation on the same shaft 32 with an insulating coupling 33 between them, and controlled by a single control knob 34.

With the above described arrangement a single .control knob is utilized for varying the volume or output of the apparatus, thus entirely eliminating the confusion heretofore experienced by the user of such apparatus when confronted by two volume controls, one of which is always inoperative. F urthermore, the range of operation for either phonograph or radio is the same, which is a desirable feature, and the potentiometers are connected as indicated so that their maximum and minimum points will coincide, that is the volume will increase in the same direction in either case.

A practical construction of the dual control means is shown in Figs. 2 and 3 to which attention is now directed. 35 and 36 are du plicate insulating bodies adapted to receive circular or semi-circular resistance strips 37 and 38 respectively, 38 in the present example being that for the phonograph control and 37 being for radio control. The insulating bodies are provided with suitable central bearing means 39 which are aligned for receiving a common shaft 40 on which are mounted spring contact arms 41 for engaging the resistance strips 37 and 38. The bodies are held in alignment with each other by a suitable spacer 42 and two bolts 43 and between the potentiometers in the shaft 40 is inserted an insulating coupling 44 of suitable construction.

For electrical connections each resistor or potentiometer is provided with end terminals 45 and a center terminal 46 which is connected with the moving arm or contact through a contact strip 47.

One end ofshaft 40 is provided with a control knob 48 which is adapted to be located on the panel face of the apparatus while the potentiometer itself is concealed behind the latter. A bent strip frame 49 held at its ends by bolts 43 serves as a simple mounting means in connection with the instrument or apparatus panel which is indicated at 50.

It will be noted in the construction of the double resistor or potentiometer, that the tiometers with the exception of the resistance strips which are wound to different values, and the shaft which is common to both and which in certain installations may be provided without the insulating coupling means. A simple frame, and insulated coupling in the present example, completes the assembly. In practice this construction has not only simplified the operation and appearance of radio-phonograph combinations but has resulted in a considerable saving in cost because of its simplicity.

It will be noted that with the type of volume control shown in the present example, the potentiometers are placed back to back with the contact arms facing outwardly. With a duplicate construction throughout, this arrangement causes the contact arm 41 on one potentiometer to bend 1n one direction (Fig. 3), while the contact arm of the other potentiometer bends in the opposite a direction. This gives the same smooth operation in either direction of movement of the control knob and is the preferred arrangement for that reason.

It should be understood that while the arrangement shown and described is that which is at present preferred, that the invention is not limited thereto, but may be carried out in connection with any radio-phonograph combination, the essential feature being to bring the control means for radio and for phonograph volume into the same movement range and to connect the two together for simultaneous operation through this range by a single control means thereby materially simplifying the construction and operation and efiecting a saving in the cost of construction.

What I claim as new and desire to secure by Letters Patent of the United States, is:

g 1. In a radio-phonograph apparatus,

means for controlling the radio volume, separate means for controlling the phonograph volume, said radio and phonograph control means being variable through the same movement range between difiering maximum and minimum values, and a common control means for varying said means simultaneously through said range.

2. The combination with a radio-phonou graph apparatus, of a dual volume control means comprising a pair of potentiometers having differing electrical resistances, and a single-control means connected with said otentiometers for operating them through any the same movement range.

' 3. The combination with an apparatus embodying a radio receiving circuit and a phonograph pick-up circuit, of a dual volume control means comprising a variable resistor 25 in each of said circuits, and a single control means for varying said resistors simultaneously through the same movement range.

4. A volume control means for an appa- 'ratus embodyin a radio recei circuit 80 and a dphonograp pick-u circuit, said means inclu 'ng a single contro panel knob, a shaft connected therewith, and a pair of variable resistors mounted on the shaft for simultaneous operation through the same move- 3| ment range, one of said resistors being arranged to control said radio receivin cir- "cuit and the other of said, resistors ing arranged to control said phonograph pickup circuit.

40 5. A volume control means for a combination radio receiver and phono a h com rising a single panel knob, a s a on w ich sa1d knob is mounted, a radio volume control and a phonograph volume control device each 45 mounted on said shaft to be operated simultaneously by movement thereof, said devices having the same movement range between their maximum and control limit?n (11 6. a ra 'o-phono ph a aratus means connected in one cid uit of ill; appa ratus for controlling the radio volume, means connected in another circuit of the apparatus for controlling the phonograph volume said radio and phonograph control means ing, variable through the same movement ran a between their maximum and minimum v5- ues, and a common control means for va said means simultaneously through said range.

In witness whereof, I have hereunto set my hand this 25th day of September, 1928. DOW O. WHELAN. 

